In copending application Ser. No. 125,869, filed Feb. 29, 1980, there is disclosed a novel cleaning body for on-line usage in removing foreign materials from the internal surface of tubes of a shell and tube-type heat exchanger, such as a surface condenser. The cleaning body is comprised of a spherically-shaped core of an elastomeric material from which extend a plurality of radially extending filaments of an elastomeric material.
The use of cleaning bodies for heat transfer systems has been described, inter alia, in U.S. Pat. Nos. 1,795,348 to Schmidt; 2,801,824 and 3,021,117 to Taprogge; and 3,215,195 and 4,113,008 to Treplin. In such later references, the cleaning bodies are formed to an elastomeric material, such as sponge rubber having a diameter at least as great as the internal diameter of the tubes being cleaned, and preferably of a greater diameter. In addition to the problems arising from normal usage of sponge balls e.g. deaeration, short life periods and tendencies to collect in dead spots, the use of sponge balls also present problems of separation from the fluid, plugging of tubes due to lodged debris, etc. Separation is of particular concern, for ineffective separation, i.e. lost and discharge of the sponge balls from the system reduces cleaning efficiency.
In accordance with such aforementioned references, diverse intercepting means are employed in a conduit downstream of the tubular heat exchange to separate the cleaning bodies from the fluid in which said bodies are suspended, e.g. an inclined screen, a conically-shaped screen assembly including ring members, etc. The number of sieves or screens is determined by the diameter of the conduit and the diameter of the cleaning bodies with inclination being a function of fluid velocity and the relative hardness of the cleaning bodies.
The sieve or screen members are formed of bars or wire members spaced apart a distance substantially less than the diameter of the cleaning bodies and disposed at an inclined angle to fluid flow to permit the cleaning bodies to roll down the inclined surface to a collection zone from which the cleaning bodies are returned to the upstream side of the tubular heat exchanger of the heat exchanger system. Thus, the cleaning bodies are caused to roll down the sieve in contact with adjacent bar members, i.e. the cleaning bodies have a tendency to roll between the bar members, an area through which the fluid also flows. Such bar members are generally formed of rectangular stock, but have also been formed of other shapes, e.g. T-shaped bar stock, square-shaped bar stock, tapered bar stock, etc.
With the use of cleaning members formed of sponge rubber, fluid velocities through the sieve assembly are limited by the locking of such sponge bodies to the sieve by distortion of the cleaning body thereby, encountering difficulty in maintaining cleaning body circulation. For sponge rubber cleaning bodies having a diameter of about 1 inch, i.e. for cleaning tubes having an internal diameter of 0.9 inches, the spacing or gap between adjacent bar or wire member of the sieve assembly is in the order of 0.39 inches. The open area of the sieve and the pressure loss thru and across the sieve assembly, is affected by the inclination of the sieve assembly, the bar width and the gap. The pressure loss of clean sieves is the lowest obtainable for each particular design with pressure loss increasing as debris accumulates on the sieve bars and is locked in place on top of or in the sieve bars due to the velocity of the circulating fluid and the nature of the debris.
Accumulated debris is periodically removed from the sieve assembly by rotating sub-assemblies forming the sieve assembly and thereby backwashing the screen assembly since accumulated debris is detrimental to the circulation of the cleaning bodies. Sponge cleaning bodies have a tendency to accumulate behind the debris and or adhere to the screen assembly in a manner such that the periodic backwashing of debris concomitantly results in cleaning body losses with reduced cleaning effectiveness.
Since uniform fluid velocity is difficult to achieve across all parts of the screen assembly, fluid velocities are obtained which exceed the allowable limits for particular diameters, hardness, hardness with respect to bar gap, etc. thereby resulting in the penetration through the screen assembly of sponge cleaning bodies or at least their adherence thereto with or without debris accumulation. As hereinabove discussed, the screen assemblies result in the cleaning bodies rolling between or straddling adjacent bars which is detrimental to rolling movement since point contact on each of the bars allows for high deformation of sponge cleaning balls and creates a pivoting action which is frictionally resistant to rolling.